Bridge and Method for Optimization of Memory for Ethernet OAM Multicast Frames

ABSTRACT

A bridge (EthOAM device) and method are described herein where the bridge implements the method and reduces a number of static entries (pre-defined multicast MAC addresses) which need to be configured within a database (e.g., forwarding database (FDB)) to support the flow of Ethernet OAM multicast frames such as, for example, Connectivity Check (CC) frames and Link Trace (LT) frames which are used in accordance with the IEEE 802.1ag standard.

CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/870,869 filed on Dec. 20, 2006 and entitled “Optimization ofMemory for EthOAM Multicast Entries”. The contents of this document arehereby incorporated by reference herein.

TECHNICAL FIELD

The present invention is related to a bridge and method for reducing anumber of static entries which need to be configured within a databaseto support the flow of Ethernet OAM multicast frames such as, forexample, Connectivity Check (CC) frames and Link Trace (LT) frames whichare used in accordance with the IEEE 802.1ag standard.

BACKGROUND

The following abbreviations are herewith defined, at least some of whichare referred to in the ensuing description of the prior art and thepresent invention.

CC Continuity Check CFM Connectivity Fault Management DSAP DomainService Access Point FDB Forwarding Database IEEE Institute ofElectrical and Electronics Engineers MA Maintenance Association MACMedia Access Control MD Maintenance Domain MEP Maintenance End Point MHFMIP Half Function MIB Management Information Base MIP MaintenanceIntermediate Point MP Maintenance Point LT Link Trace LTR Link TraceReply OAM Operation, Administration and Maintenance PDB PermanentDatabase PDU Protocol Data Unit RAM Random Access Memory SNMP SmallNetwork Management Protocol VLAN Virtual Local Area Network

Referring to FIG. 1 (PRIOR ART), there is a block diagram of atraditional bridge 100 which implements an IEEE 802.1ag standard that isused to help explain a problem with needing to configure a large numberof static entries within a permanent database for pre-defined multicastMAC addresses associated with CC multicast frames and LT multicastframes. The traditional bridge 100 by implementing the IEEE 802.1agstandard is able to provide a connectivity fault management which isuseful for detecting, isolating and reporting connectivity faults withinEthernet networks. The IEEE 802.1ag standard is well known to thoseskilled in the art but to aid in the understanding of the presentdiscussion several of the key terms which are used herein and theirdefinitions are provided below:

CC message: A multicast CFM PDU transmitted periodically by a MEP toassure the continuity over the MA to which the transmitting MEP belongs.No reply is sent by any MP in response to receiving a CCM.

Customer: A consumer of an Ethernet Service. The customer might lease apoint to point or multipoint connection to a network provider. Thecustomer is the final user of the Ethernet service.

LT message: A CFM PDU initiated by a MEP to trace a path to a target MACaddress, forwarded from MIP to MIP, up to the point at which the LTMreaches its target, a MEP, or can no longer be forwarded. Each MP alongthe path to the target generates an LTR.

MA: A set of MEPs, each configured with the same MAID and MD Level,established to verify the integrity of a single service instance. An MAcan also be thought of as a full mesh of Maintenance Entities among aset of MEPs so configured.

MEP: An actively managed CFM entity, associated with a specific DSAP ofa service instance, which can generate and receive CFM PDUs and trackany responses. It is an end point of a single MA, and is an endpoint ofa separate Maintenance Entity for each of the other MEPs in the same MA.

MIP: A CFM entity consisting of two MHFs. MIPs are not activelymonitored and are configured at intermediate points in the Ethernetservice instance.

Operator: An operator owns equipment used to create L2 or L3 networks.The operator can lease a subset of its network to providers. Theoperator (network operator) can, in fact, be identical to, or a part ofthe same organization as, the service provider, but for purposes of thisdiscussion, the operator and service provider are presumed to beseparate organizations.

Provider: A provider does not actually own all its equipment but canmanage limited functionalities of its Ethernet services leased to anoperator. The provider can also act as a provider if it owns and iswilling to lease Ethernet services.

Owner: An owner of a system (and in particular, a Bridge) is a user whohas full access to the System Group of the SNMPv2-MIB.

For a more detailed discussion about the IEEE 802.1ag standard,reference is made to the current IEEE 802.1ag/D8 standard entitled“Local and Metropolitan Area Networks-Virtual Bridged Local AreaNetworks-Amendment 5: Connectivity Fault Management” dated Feb. 8, 2007.The contents of this document are hereby incorporated by referenceherein.

The traditional bridge 100 has a processor 102 that supports the flow ofmulticast frames such as CC and LT multicast frames and terminate the CCand LT multicast frames because it has previously configured pre-definedmulticast MAC addresses which correspond to the CC and LT multicastframes at the appropriate level as permanent static entries within afiltering database 104 (FDB 104). The region within the FDB 104 that isoccupied by the static entries is called the permanent database 106 (PDB106). The traditional bridge 100 pursuant to the IEEE 802.1ag standardcan support upto 4094 VLANs and eight levels where the eight levels areorganized as follows: (1) customers can be assigned levels 7 or 6; (2)providers can be assigned levels 5, 4 and 3; and (3) operators can beassigned levels 2, 1 and 0 (see the aforementioned definitions of thecustomers, providers and operators).

Plus, the traditional bridge 100 pursuant to the IEEE 802.1ag standardreserves upto eight multicast MAC addresses for CC multicast frames (onefor each level) and upto eight multicast MAC addresses for LT multicastframes (one for each level). The eight multicast MAC addresses for theCC multicast frames and the eight multicast MAC addresses for the LTmulticast frames are all pre-defined/reserved in the current IEEE802.1ag standard as follows:

TABLE 1 01-80-C2-xx-xx-xy MD Level of CC message Four address bits “y” 77 6 6 5 5 4 4 3 3 2 2 1 1 0 0

TABLE 2 01-80-C2-xx-xx-xy MD Level of LT message Four address bits “y” 7F 6 E 5 D 4 C 3 B 2 A 1 9 0 8

In operation, the traditional bridge 100 upon receiving a CC multicastframe or LT multicast frame takes their destination multicast MACaddress and performs a table look-up operation in the PDB 106 and ifthere is a previously stored static entry with the same multicast MACaddress then the received CC multicast frame or LT multicast frame isterminated and further processed within the bridge's software (note: thelevel of the received CC multicast frame or the LT multicast frame isencoded in the last four bits of the multicast MAC address).

However, the traditional bridge 100 by needing to support upto 4094VLANs and upto eight levels for both CC and LT multicast frames meansthat the number of static entries that may need to be configured in thePDB 106 so as to store the CC and LT reserved multicast MAC addressescan be as high as (4094×8)×2=655504. Unfortunately, most traditionalbridges 100 do not have enough space to support and store such a largenumber of static entries within their PDB 106. An example is providednext to help illustrate how the traditional bridge 100 needs toconfigure the static entries within the PDB 106 for both the CC and LTreserved multicast MAC addresses for each supported VLAN. In thisexample, assume the traditional bridge 100 supports five maintenanceassociations (MAs) as follows:

MA1 VLAN 100 Level 5 MA2 VLAN 50 Level 5 MA3 VLAN 40 Level 4 MA4 VLAN 30Level 3

To configure MA1 which is associated with VLAN 100 at level 5, thetraditional bridge 100 (e.g., traditional MEP 100) would create sixstatic entries within the PDB 106 for the reserved CC multicast MACaddresses associated with levels 5 through 0 and also create six staticentries within the PDB 106 for the reserved LT multicast MAC addressesassociated with levels 5 through 0. These twelve static entries areillustrated as elements 1-12 within TABLE 3.

To configure MA2 which is associated with VLAN 50 at level 5, thetraditional bridge 100 (e.g., traditional MEP 100) would create sixstatic entries within the PDB 106 for the reserved CC multicast MACaddresses associated with levels 5 through 0 and also create six staticentries within the PDB 106 for the reserved LT multicast MAC addressesassociated with levels 5 through 0. These twelve static entries areillustrated as elements 13-24 within TABLE 3.

To configure MA3 which is associated with VLAN 40 at level 4, thetraditional bridge 100 (e.g., traditional MEP 100) would create fivestatic entries within the PDB 106 for the reserved CC multicast MACaddresses associated with levels 4 through 0 and also create five staticentries within the PDB 106 for the reserved LT multicast MAC addressesassociated with levels 4 through 0. These ten static entries areillustrated as elements 25-34 within TABLE 3.

To configure MA4 which is associated with VLAN 30 at level 3, thetraditional bridge 100 (e.g., traditional MEP 100) would create fourstatic entries within the PDB 106 for the reserved CC multicast MACaddresses associated with levels 3 through 0 and also create four staticentries within the PDB 106 for the reserved LT multicast MAC addressesassociated with levels 3 through 0. These eight static entries areillustrated as elements 35-52 within TABLE 3.

TABLE 3 Static Entry Vlan ID Multicast MAC Address 1 100 CC 5 2 100 CC 43 100 CC 3 4 100 CC 2 5 100 CC 1 6 100 CC 0 7 100 LT 5 8 100 LT 4 9 100LT 3 10 100 LT 2 11 100 LT 1 12 100 LT 0 13 50 CC 5 14 50 CC 4 15 50 CC3 16 50 CC 2 17 50 CC 1 18 50 CC 0 19 50 LT 5 20 50 LT 4 21 50 LT 3 2250 LT 2 23 50 LT 1 24 50 LT 0 25 40 CC 4 26 40 CC 3 27 40 CC 2 28 40 CC1 29 40 CC 0 30 40 LT 4 31 40 LT 3 32 40 LT 2 33 40 LT 1 34 40 LT 0 3530 CC 3 36 30 CC 2 37 30 CC 1 38 30 CC 0 39 30 LT 3 40 30 LT 2 41 30 LT1 42 30 LT 0 Note: CCx: Reserved multicast MAC address for CC for levelx. LTx: Reserved multicast MAC address for LT for level x.

Accordingly, there has been and is a need to provide a solution whichcan be implemented by a bridge to reduce the number of static entriesthat need to be configured in the PDB 106 while still being able tosupport 4094 VLANs and 8 Levels. This need and other needs are satisfiedby the present invention.

SUMMARY

In one aspect, the present invention provides a method for reducing anumber of static entries which need to be configured within a databaseof a bridge. The method includes the steps of: (1) forming one or moreVLAN sets where each VLAN set contains one or more VLAN(s) that areconfigured at a same level; (2) creating a list of supported levels; (3)configuring a static entry within the database for each reservedmulticast address for a lowest supported level and all lesser levelsthrough zero which correspond with the VLAN(s) in the VLAN set at thelowest supported level; (4) removing a current lowest supported levelfrom the list of supported levels; (5) configuring a static entry withinthe database for each reserved multicast address for the current lowestsupported level through a highest level so far configured plus one whichcorrespond with the VLAN(s) in the VLAN set at the current lowestsupported level; and (6) repeating the removing step (4) and the secondconfiguring step (5) until the list of supported levels is empty.

In yet another aspect, the present invention provides a bridge (e.g.,EthOAM entity) with a processor and memory with instructions storedtherein which are processable by the processor to reduce a number ofstatic entries that need to be stored within a database by: (1) formingone or more VLAN sets where each VLAN set contains one or more VLAN(s)that are configured at a same level; (2) creating a list of supportedlevels; (3) configuring a static entry within the database for eachreserved multicast address for a lowest supported level and all lesserlevels through zero which correspond with the VLAN(s) in the VLAN set atthe lowest supported level; (4) removing a current lowest supportedlevel from the list of supported levels; (5) configuring a static entrywithin the database for each reserved multicast address for the currentlowest supported level through a highest level so far configured plusone which correspond with the VLAN(s) in the VLAN set at the currentlowest supported level; and (6) repeating the removing step (4) and thesecond configuring step (5) until the list of supported levels is empty.

Additional aspects of the invention will be set forth, in part, in thedetailed description, figures and any claims which follow, and in partwill be derived from the detailed description, or can be learned bypractice of the invention. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory only and are not restrictive of the inventionas disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be obtainedby reference to the following detailed description when taken inconjunction with the accompanying drawings wherein:

FIG. 1 (PRIOR ART) is a block diagram illustrating the basic componentsof a traditional bridge which is used to help explain a problem withneeding to configure a large number of static entries within a databasethat is addressed by the present invention;

FIG. 2 is a block diagram illustrating the basic components of a bridgewhich has been configured to reduce the number of static entries thatneed to be configured within a database in accordance with the presentinvention; and

FIG. 3 is a flowchart illustrating the basic steps of a method forreducing the number of static entries that need to be configured withinthe database of a bridge in accordance with the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 2 and 3, there are respectively shown a block diagramof a bridge 200 and a flowchart of a method 300 that is implemented bythe bridge 200 to reduce the number of static entries which need to beconfigured in a FDB 202 (in particular a PDB 204) in accordance with thepresent invention. In particular, the bridge 200 has a memory 206 (e.g.,RAM memory 206) which stores instructions that are processable by aprocessor 208 to facilitate the various steps of the memory optimizationmethod 300 as follows:

Step 1: Form one or more VLAN sets (e.g., Vx, Vy, Vz) where each VLANset contains one or more VLAN(s) that are configured at a same level(see step 302 in FIG. 3). In particular, the VLANs that are at the samelevel can be grouped into a VLAN set as follows:

Vx={Vx1, Vx2, . . . , Vxn} where Vx=VLANs configured for level xVy={Vy1, Vy2, . . . , Vyn} where Vy=VLANs configured for level yVz={Vz1, Vz2, . . . , Vzn} where Vz=VLANs configured for level z wherex>y>z. Step 2: Create a list of the levels supported by the bridge 200and find the smallest level in this list (z) (see step 304 in FIG. 3).

Step 3: Configure a static entry within the PDB 204 for eachpre-defined/reserved CC and LT multicast MAC address for the lowestsupported level (z) and all lesser levels through zero which correspondwith the VLAN(s) in the VLAN set at the lowest level (z) (see step 306in FIG. 3).

Step 4: Remove the current lowest level from the list of supportedlevels (see step 308 in FIG. 3).

Step 5: Configure a static entry within the PDB 204 for eachpre-defined/reserved CC and LT multicast MAC address at the currentlowest supported level through a highest level so far configured plusone which correspond with the VLAN(s) in the VLAN set at the currentlowest supported level (see step 310 in FIG. 3).

Step 6. Repeat Steps 4 and 5 until the list of supported levels is empty(see steps 312 and 314 in FIG. 3).

A graphical result of this optimization is shown below in TABLE 4.

TABLE 4 MAC Addresses to be Number of Multicast VLAN set ConfiguredEntries {Vx, VY, Vz} CCz, CCz-1, . . . , CC0 2 (z + 1) LTz, LTz-1, . . ., LT0 {Vx, Vy} CCy, CCy-1 . . . CCy-(y-z-1) 2 (y − z) LTy, LTy-1 . . .LTy-(y-z-1) {Vx} CCx, CCx-1, . . . , CCx- 2 (x − y) (x-y-1) LTx, LTx-1,. . . , LTx- (x-y-1)

This table should be read as follows: For the first row, these MACaddresses (CCz, CCz−1, . . . , CC0 and LTz, LTz−1, . . . , LT0) need tobe configured in PDB 204 for VLAN set {Vx, Vy, Vz}. In the second row,these MAC addresses (CCy, CCy−1, . . . , CCy−(y−Z−1) and LTy, LTy−1, . .. , LTy−(y−Z−1)) need to be configured in PDB 204 for VLAN set {Vx, Vy}.In the third row, these MAC addresses (CCx, CCx−1, . . . , CCx−(x−y−1)and LTx, LTx−1, . . . , LTx−(x−y−1)) need to be configured in PDB 204for VLAN set {Vx}.

As can be seen, the present invention is a marked improvement over theprior art since the total number of static entries that need to beconfigured in memory with optimization=2 (z+1+y−z+x−y)=2x+2. While, thetotal number of static entries that need to be configured in memorywithout optimization=[(2*#of VLANs at level z*(z+1))+(2*#of VLANs atlevel y*(y+1))+(2*#of VLANs at level z*(x+1))]. This savings isillustrated below by using the same example that was discussed abovewith respect to the prior art but now the memory optimization method 300of the present invention is used to configure the static entries in thePDB 204 of the bridge 200.

In this example, assume the bridge 200 supports five maintenanceassociations (MAs) as follows:

MA1 VLAN 100 Level 5 MA2 VLAN 50 Level 5 MA3 VLAN 40 Level 4 MA4 VLAN 30Level 3Step 1: Group the VLANs that are at the same level as follows:

V5={VLAN100, VLAN50}

V4={VLAN40}

V3={VLAN30}

where Vx: is the Vlan at level x (see step 302 in FIG. 3).

Step 2: Create a list of the supported levels {5,4,3} and find thesmallest level {3} in this list (see step 304 in FIG. 3).

Step 3: Configure a static entry within the PDB 204 for eachpre-defined/reserved CC and LT multicast MAC address for the lowestsupported level {3} and all lesser levels through zero which correspondwith the VLAN(s) in the VLAN set V3 (note: the eight configured staticentries are illustrated as elements 1-8 in TABLE 4) (see step 306 inFIG. 3).Step 4: Remove the current lowest level {3} from the list of supportedlevels. Thus, the smallest level now in the list is level {4} (see step308 in FIG. 3).Step 5: Configure a static entry within the PDB 204 for eachpre-defined/reserved CC and LT multicast MAC address at the currentlowest supported level {4} through a highest level so far configuredplus one {3+1} which correspond with the VLAN(s) in the VLAN set V4(note: the two configured static entries are illustrated as elements9-10 in TABLE 4) (see step 310 in FIG. 3).Step 6A (repeat step 4): Remove the current lowest level {4} from thelist of supported levels. Thus, the smallest level now in the list islevel {5} (see step 312 and step 308 (second time) in FIG. 3).Step 6B (repeat step 5): Configure a static entry within the PDB 204 foreach pre-defined/reserved CC and LT multicast MAC address at the currentlowest supported level {5} through a highest level so far configuredplus one {4+1} which correspond with the VLAN(s) in the VLAN set V5(note: the two configured static entries are illustrated as elements11-12 in TABLE 4) (see step 310 (second time) in FIG. 3).

Step 7: The memory optimization method 300 is stopped since the list oflevels is now empty (see step 314 in FIG. 3).

The results of performing steps 1-7 for this particular example areillustrated in TABLES 5 and 6:

TABLE 5 Static Entry VLAN Set Multicast MAC Address 1 {100, 50, 40, 30}CC 3 2 {100, 50, 40, 30} CC 2 3 {100, 50, 40, 30} CC 1 4 {100, 50, 40,30} CC 0 5 {100, 50, 40, 30} LT 3 6 {100, 50, 40, 30} LT 2 7 {100, 50,40, 30} LT 1 8 {100, 50, 40, 30} LT 0 9 {100, 50, 40} CC 4 10 {100, 50,40} LT 4 11 {100, 50} CC 5 12 {100, 50} LT 5

TABLE 6 MAC Addresses to Number of multicast VLAN set be Configuredentries (V5, V4, V3) CC3, CC2, CC1, CC0 8 LT3, LT2, LT1, LT0 (V5, V4)CC4, LT4 2 (V5) CC5, LT5 2

As can be seen in TABLES 5 and 6, the total number of static entriesconfigured in the PDB 204 is 12 (elements 1-12). In contrast, in theprior art example 42 static entries had to be configured in the PDB 106as shown in TABLE 3. Thus, the number of configured static entries hasbeen reduced by 42−12=30. In this particular example, this results inmemory savings of 75%.

From the foregoing, it can be readily appreciated by those skilled inthe art that the present invention provides a memory optimization method300 that reduces the amount of memory needed to store the static entriesthat are associated with EthOAM by: (1) identifying groups of VLANs thatare at the same level; and (2) storing them all in one entry as follows:<VLAN x, VLAN y, VLAN p, reserved MAC address G>. This is done for everygroup of VLAN, starting from the lowest level. In contrast, in the priorart a separate entry needed to be stored for each VLAN as follows: <VLANx, MAC G>, <VLAN y, MAC G>, <VLAN p, MAC G>. The memory optimizationmethod 300 can be implemented in any bridge 200 that has amicroprocessor RAM which can store entries in the format <VLANx, VLANy,VLANZ, MAC>. Thus, the bridge 200 after configuring the static entriesin the PDB 204 can receive an incoming frame and perform the followingoperations: (1) determine the VLAN (there is no need to know the level);(2) look-up the PDB 204 and check if the destination MAC address in theincoming frame matches any of the stored multicast MAC destinationaddresses; and (3) if there is a match then terminate the incomingframe.

Although one embodiment of the present invention has been illustrated inthe accompanying Drawings and described in the foregoing DetailedDescription, it should be understood that the invention is not limitedto the embodiment disclosed, but is capable of numerous rearrangements,modifications and substitutions without departing from the spirit of theinvention as set forth and defined by the following claims.

1. A method for reducing a number of static entries which need to beconfigured within a database of a bridge, said method comprising thesteps of: forming one or more Virtual Local Area Network (VLAN) setswhere each VLAN set contains one or more VLAN(s) that are configured ata same level; creating a list of supported levels; configuring a staticentry within said database for each reserved multicast address for alowest supported level and all lesser levels through zero whichcorrespond with the VLAN(s) in the VLAN set at the lowest supportedlevel; removing a current lowest supported level from the list ofsupported levels; configuring a static entry within said database foreach reserved multicast address for the current lowest supported levelthrough a highest level so far configured plus one which correspond withthe VLAN(s) in the VLAN set at the current lowest supported level; andrepeating said removing step and said second configuring step until thelist of supported levels is empty.
 2. The method of claim 1, whereinsaid database is a permanent database in a filtering database.
 3. Themethod of claim 1, wherein said reserved multicast address is associatedwith a Connectivity Check multicast address.
 4. The method of claim 1,wherein said reserved multicast address is associated with a Link Tracemulticast address.
 5. The method of claim 1, wherein said bridge is aMaintenance End Point (MEP) that supports a connectivity faultmanagement protocol which includes Connectivity Check multicast framesand Link Trace multicast frames.
 6. The method of claim 1, wherein saidbridge is a Maintenance Intermediate Point (MIP) that supports aconnectivity fault management protocol which includes Connectivity Checkmulticast frames and Link Trace multicast frames.
 7. The method of claim1, wherein said bridge supports an IEEE P802.1ag protocol.
 8. A bridge,comprising: a processor; a memory; and instructions which are accessiblefrom said memory and processable by said processor to reduce a number ofstatic entries that need to be stored within a database by: forming oneor more Virtual Local Area Network (VLAN) sets where each VLAN setcontains one or more VLAN(s) that are configured at a same level;creating a list of supported levels; configuring a static entry withinsaid database for each reserved multicast address for a lowest supportedlevel and all lesser levels through zero which correspond with theVLAN(s) in the VLAN set at the lowest supported level; removing acurrent lowest supported level from the list of supported levels;configuring a static entry within said database for each reservedmulticast address for the current lowest supported level through ahighest level so far configured plus one which correspond with theVLAN(s) in the VLAN set at the current lowest supported level; andrepeating said removing step and said second configuring step until thelist of supported levels is empty.
 9. The bridge of claim 8, whereinsaid database is a permanent database in a filtering database.
 10. Thebridge of claim 8, wherein said reserved multicast address is associatedwith a Connectivity Check multicast address.
 11. The bridge of claim 8,wherein said reserved multicast address is associated with a Link Tracemulticast address.
 12. The bridge of claim 8, wherein said processorsupports a connectivity fault management protocol which includesConnectivity Check multicast frames and Link Trace multicast frames. 13.The bridge of claim 8, wherein said processor supports an IEEE P802.1agprotocol.
 14. An Ethernet Operation, Administration and Maintenance(OAM) device, comprising: a processor which supports a connectivityfault management protocol; a memory; and instructions which areaccessible from said memory and processable by said processor to reducea number of static entries within a permanent database by: forming oneor more Virtual Local Area Network (VLAN) sets where each VLAN setcontains one or more VLAN(s) that are configured at a same level;creating a list of supported levels; configuring a static entry withinsaid database for each reserved multicast MAC address including aConnectivity Check multicast address and a Link Trace multicast addressat a lowest supported level and all lesser levels through zero whichcorrespond with the VLAN(s) in the VLAN set at the lowest supportedlevel; removing a current lowest supported level from the list ofsupported levels; configuring a static entry within said database foreach reserved multicast address including a Connectivity Check multicastaddress and a Link Trace multicast address for the current lowestsupported level through a highest level so far configured plus one whichcorrespond with the VLAN(s) in the VLAN set at the current lowestsupported level; and repeating said removing step and said secondconfiguring step until the list of supported levels is empty.
 15. TheEthernet OAM device of claim 14, wherein said connectivity faultmanagement protocol is associated with an IEEE P802.1ag protocol.